The present invention relates generally to voltage-controlled tuning systems for television receivers and, more particularly, to a tuner circuit for tuning all VHF and CATV channels including those having carrier frequencies in the low VHF band, the mid/high VHF band, the CATV superband and the so-called CATV hyperband.
The present U.S. television signal spectrum for VHF and CATV channels can be divided into three bands; a low VHF band extending between 54-88 MHz and including VHF channels 2-6, a mid/high VHF band extending between 120-216 MHz and including CATV channels A-I and VHF channels 7-13 and a CATV superband extending between 216-300 MHz and including CATV channels J-W. There has recently been much interest in extending the CATV frequency spectrum beyond the present superband to a so-called hyperband which includes 18 CATV channels in the band of carrier frequencies between 300-400 MHz. There is presently no known television receiver tuning system on the market capable of covering this extended CATV spectrum other than those systems utilizing an additional tuner (i.e. a CATV converter) which converts all CATV signals to a signal corresponding to one of the low VHF channels.
Co-pending application Ser. No. 132,348 filed Mar. 20, 1980, now U.S. Pat. No. 4,271,529 and assigned to the assignee of the present invention, which application is incorporated herein by reference, discloses a VHF/CATV tuning system in which a single tuning circuit is used to tune all VHF and CATV channels in the low VHF band, the mid/high VHF band and the CATV superband. The tuning circuit includes a plurality of tunable resonant circuits each comprising a voltage-controlled variable capacitance diode, commonly referred to as a varactor diode, and an arrangement of three inductors connected thereto. A pair of band switching diodes are also connected in the circuit, the switching diodes being operative in response to suitable bandswitching signals for connecting three different combinations of the inductors across the varactor diode to achieve a different resonant condition for tuning each of the three different bands. Since three different reactance elements, i.e. the three inductors, are included in the resonant circuit, the resonant circuit may be suitably aligned for tuning each of the three different bands by suitably adjusting the inductance of an appropriate one of the inductors. The foregoing resonant circuit does not, however, enable proper tuning of an additional fourth band of channels such as the CATV hyperband initially because there is no teaching with regard to establishing the necessary fourth resonant condition and, secondly, because there is no facility for aligning the circuit for properly tuning the additional band.
It is, accordingly, an object of the present invention to provide a novel multi-band television receiver tuning system capable of tuning all VHF and CATV channels including those having carrier frequencies in the so-called hyperband extending between 300-400 MHz.
Another object of the invention is to provide a single, easily aligned, all channel, voltage-controlled tuning system for operation over all VHF bands as well as all CATV bands including the hyperband.